In the journal called "Technische Mitteilungen des RFZ" 22nd year, number 1, pages 4-7 a method is described in which the figure which is to be wiped as a special effect is created by combining a plurality of input signal sequences, each having a predetermined variation with respect to time. The input signals are generated in so called function generators which are synchronized by either the horizontal or vertical synchronization signals. After the signals have been combined, they are applied to a voltage comparator. The size of the figure to be wiped can be adjusted by changing the limit at which the voltage comparator becomes effective. In order to adjust the position of the figure on the screen, continuously adjustable delay stages are provided which delay the input signals relative to the synchronization signal to which the function generator which generates it is synchronized.
This known method has the disadvantage that, when the position of the figure is adjusted past a particular edge of the screen, that portion of the figure which has been pushed past the edge will reappear at the opposite edge. In the German publication DAS Nos. 2222150 and 2456745 circuits are described which prevent this undesired appearance of the figure. However, these circuits in turn introduce another error. Specifically, shifting of the figure changes the boundaries of the region near the edge of the screen where limiting during a fadeover is masked, so that these boundaries are shifted into the picture area.